Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 111

From the ease with which it gives up its third atom of oxygen, ozone has been proposed when mixed with air, as a means of decolorising wax, stearin, and other organic substances which cannot be subjected to the fumes of sulphurous acid or chlorine, or at any rate only partially so.

Ozone does not appear, however, to have been much, if at all adopted, for bleaching the above products, which are still, we believe, mostly whitened by the old method of exposure to the air.

Being one of the most energetic oxidising agents known, it is not surprising that the claims of ozone as a disinfectant should have found many supporters. One of its strongest advocates for this purpose is Dr Cornelius Fox, who says,--"Ozone should be diffused through fever-wards, sick rooms, the crowded localities of the poor, or wherever the active power of the air is reduced and poisons are generated. Its employment is especially demanded in our hospitals, situated as they mostly are in densely populated districts, where the atmosphere is almost always polluted by rebreathed air, decomposing substances and their products, and where no mere ventilation can be fully effective. If practicable, it would be highly advantageous to direct streams of sea-air, or air artificially ozonised into the fever and cholera nests of our towns. Ozone may be easily disseminated through public buildings, theatres, and other confined atmospheres, where numbers of people are accustomed to a.s.semble in order to maintain the purity of the air."

Another ardent believer in the hygienic value of ozone is Linder, who is also a strong advocate for its medical application, and recommends it both in the form of ozonised air and water in tuberculosis, rheumatism, asthma, and many other diseases. Linder, it is said, has set up an ozone manufactory, and vends ozone inhalations by the cubic foot.

To the contention of those who a.s.sert that it is impossible to convey such an unstable body as ozone into the blood without the ozone becoming decomposed into ordinary oxygen, this instability is denied upon the authority of Lehone and Hozeau, who state that it is less liable to change than is generally supposed, for they found, after working with it, that its peculiar odour remained on their hands and garments for some time.

These views, largely shared by many others, as to the beneficial effects of ozone have, however, not been allowed to pa.s.s unchallenged. M. P.

Thenard considered it important that both the public and medical men should be apprised of the erroneous character of the opinions generally entertained respecting the action of ozone on the organism. Ozone, he says, so far from exerting a beneficial effect, is one of the most energetic of poisons; and the serious accidents which have occurred in his own laboratory do not leave the slightest room for doubt in the matter.

Writing to the 'Comptes Rendus,'[85] M. P. Thenard narrates the case of a guinea-pig, in which the beats of the pulse, normally 148 per minute, fell to 1/30th after the exposure of the animal for a quarter of an hour to an atmosphere charged with ozone. He states that under the influence of ozone, even when very largely diluted, the blood-corpuscles rapidly cohere and change their form. Other instances are recorded in which the blood, contrary to antic.i.p.ation, has been found in the venous condition.

[Footnote 85: Lx.x.xii p. 1857.]

Drs Dewar and M'Kendrick found that ozone acted as a very powerful irritant upon the mucous membranes. Further, an experiment was made by placing some small birds in a mixture of oxygen and ozone, containing 10 per cent. of the latter. In two minutes the birds were dead.

Ozone is frequently present in the atmosphere, formed by electricity and perhaps by other means. Payen states that it does not amount to more than 1/450,000th weight, and 1/70000 by volume of atmospheric air. Other observers state that it varies in amount, according to height, locality, temperature, electricity, &c. Dr Buchanan says it is more abundant "on the sea-coast than inland, in the west than in the east of Great Britain, in elevated than in low situations, with south-west than with north-east winds, in the country than in towns, and on the windward than on the leeward side of towns." According to the Scottish Meteorological Society, ozone is most prevalent in the atmosphere from February to June, when the average amount is 6, and lasts from July to January, when the average is 57. The maximum 62 is reached in May, and the minimum 53 in November.

These results are said to be in accordance with the conclusions arrived at by Dr Berigny and M. Hozeau.

Although there appears no ground for doubting that artificially prepared ozone, by reason of its actively disinfectant properties, may prove a valuable auxiliary in checking the spread of certain diseases; it seems far from satisfactorily established that the same quality is possessed by the ozone in the atmosphere, or on the contrary, as has been a.s.serted, that certain ailments are caused by it. During an outbreak of influenza at Berlin, Schonbein states that the air contained a large quant.i.ty of ozone; a circ.u.mstance confirmed by Dr Pietra-Santa during the prevalence in another locality of the same epidemic, which it was imagined might be caused by the irritating effect of the ozone on the organs of respiration.

Billard, Wolf, Bckel, and Strambis all state that, during the prevalence of cholera at Strasbourg, Berlin, and Milan ozone was absent from the atmosphere, and that the decline of the malady was marked by its reappearance. Uhle ascribes the acc.u.mulation of malaria at night to the non-formation of ozone by solar heat.

The above facts have, however, been disputed by some observers, whilst others have refused to regard them as anything more than coincidences, and have indeed cited evidence of a totally opposite character; thus Grellois has stated that he found more ozone in a marsh than elsewhere.

Mr Kingzett has shown the incorrectness of Schonbein's statement that, when oil of turpentine and other essential oils are oxidised by exposure to the air, ozone is formed. Schonbein was misled because from the oxidised oil and the air in its vicinity he obtained the ozone reaction with pota.s.sium iodide.

Mr Kingzett has demonstrated that the compound can be neither ozone nor hydrogen dioxide, because it is destroyed at the boiling point of oil of turpentine, viz. 160, at which temperature ozone and hydrogen dioxide are permanent; besides which it resists to a certain extent the action of sodium thiosulphate, and its solution in water retains its properties after long-continued boiling. Mr Kingzett believes the active properties of the oxidised turpentine oil are due to the formation of monohydrated terpene oxide (C_{10}H_{16}O.H_{2}O).

One of the most delicate tests for ozone is pota.s.sium iodide, either alone or mixed with starch. A brown colour in the former case, a blue in the latter, indicates the liberation of iodine. In the ozometer, strips of paper saturated with starch and pota.s.sium iodide are exposed to the action of a definite volume of air in a dark chamber. The comparative quant.i.ties of ozone in different samples of air are judged of by the intensity of the colour compared with a fixed scale on which 1 is the lightest and 10 generally the darkest shade. See OZONOMETER.

Ozone acts as a reducing agent in certain curious cases. Thus, hydrogen peroxide and ozone reduce one another, water and oxygen being the sole products; and some substances, such as platinum black and manganese peroxide, convert it into oxygen without suffering change themselves, being probably oxidised and reduced alternately.

=OZONOM'ETER.= This name has been given to paper prepared with a mixed solution of starch and iodide of pota.s.sium. It is white, but is turned blue by ozonised air when exposed to it in a slightly moistened state.

The following are the proportions given by Schonbein for the preparation of the paper:--1 part of _pure_ iodide of pota.s.sium, 10 parts of starch and 200 of water. Lowe gives 1 part of iodide to 5 of starch; Moffatt, 1 to 2-1/2. The best arrowroot must be used for the starch. It must be dissolved in warm water and filtered, so that a clear solution is obtained.

The iodide is dissolved in another portion of water, and gradually added.

The paper, cut in slips and previously soaked in distilled water, is placed in the mixed iodide and starch for several hours; and lastly, slowly dried in a cool dark place, the slips being hung horizontally.

Schonbein's papers require moistening with water after exposure before the trial is taken.

Payen's ozonometer, which is an improvement on the above, is made of red litmus paper with half its surface impregnated with a 1% solution of pota.s.sium iodide. The portion of the paper becomes blue by contact with air containing ozone, in consequence of oxidation and the formation of potash. The unimpregnated portion of the paper undergoes no change unless the air contains ammoniacal vapours, and then the paper becomes blue over its entire surface.

M. Davy states that he has obtained very satisfactory results in the estimation of ozone in the atmosphere, by employing a mixture of iodide of pota.s.sium and a.r.s.enite of pota.s.sium.

The value of the ozonometer as an indicator of atmospheric ozone must be looked upon as uncertain, when it is borne in mind that there are other bodies besides ozone frequently present in the air, such as nitrous acid, chlorine, &c., which give similar reactions with the above reagents.

=PACK'FONG.= _Syn._ PAKFONG, CHINESE WHITE COPPER. An alloy formed by fusing together, in a covered crucible, a.r.s.enic, 2 parts, and copper clippings, 4-1/2 to 5 parts, arranged in alternate layers, and covered with a capping of common salt. The product contains about 10% of a.r.s.enic.

_Prop., &c._ White, slightly ductile, and permanent at ordinary temperatures; at a temperature below that of redness it suffers decomposition, with the extrication of fumes of a.r.s.enious acid. Formerly much used for the scales of thermometers and other instruments, dial plates, candlesticks, &c. It is now almost superseded by the alloy of nickel and copper called German silver, to which the name is also applied by some recent writers.

=PACK'ING.= As there is considerable art in packing brittle hollow-ware, as gla.s.s, china, &c., in such a way that it will stand exposure to the jolting, blows, and agitation of land carriage, it is better, when it is of much value, or in quant.i.ty, to employ a person qualified for the job. A man accustomed to packing such articles may be readily procured at any gla.s.sworks or china warehouse for a trifling consideration. When this cannot be done, it must be recollected that the great secret of safe packing consists in the articles being carefully preserved from undue pressure or contact with each other, yet so firmly arranged, and so surrounded with some material as hay, straw, sawdust, &c., that they cannot be shaken into such a condition by the ordinary contingencies of transport. Loose packing must always be avoided.

=PAD'DING.= Among calico printers this term is applied to the operation of impregnating the pores of their cloth with a mordant. It is now almost exclusively performed by means of a simple piece of machinery (padding machine), which essentially consists of--a 'large reel,' around which the unprepared cloth is wound--a 'guide roller,' over which it pa.s.ses to smooth and adjust it before entering the liquor--a copper cylinder, or 'dip-roller,' nearly at the bottom of the 'mordant-trough,' under which it is carried from the guide-roller--a half-round polished 'stretched-bar,'

to give it equal tension--a pair of 'padded cylinders,' to remove superfluous moisture--and, lastly, a 'reel' to receive the mordanted ('padded') cloth. The degree of tension is regulated by a weight suspended on a lever, and motion is given to the whole by an endless band from the driving shaft. This machine is also applicable to many of the operations of dyeing, bleaching, and starching textile fabrics.

=PAINT'ER'S CREAM.= _Prep._ Take of pale nut oil, 6 oz.; mastic, 1 oz.; dissolve, add of sugar of lead, 1/4 oz., previously ground in the least possible quant.i.ty of oil; then further add of water, q. s., gradually, until it acquires the consistence of cream, working it well all the time.

Used by painters to cover their work when they are obliged to leave it for some time. It may be washed off with a sponge and water.

=PAINT'ING.= The art or employment of laying on colour. In the fine arts, the production of a picture or a resemblance in colours on a flat surface.

The artistic and mechanical consideration of this subject does not come within the province of our volume; but notices of the leading materials employed by both artists and house painters are given under the respective names. See the various pigments, COLOURS, OILS, VARNISHES, &c., and _below_.

=Painting, Distem'per.= A method of painting generally adopted by the ancients. Water was the princ.i.p.al medium, but various gelatinous and alb.u.minous 'binders' were added to fix the pigments. Of these the most important were glue, size, and white of egg. In modern distemper, as executed by the painters of theatrical scenery, panoramas, &c., spirit of turpentine is largely employed as a medium.

=Painting, Elydor'ic.= A method of painting invented by M. Vincent, of Montpelier, having for its object to combine the fresh appearance and finish of water colours with the mellowness of oil painting. The liquid employed as a vehicle for the pigments is an emulsion formed of oil and water by the intervention of certain portion of gum or mucilage.

=Painting, Enam'el.= In this variety of painting, vitrifiable colours are laid on thin plates of metals, and fused into it. The outline is first burnt in, after which the parts are filled up gradually, with repeated fusions at an enameller's lamp, to the most minute finishing touches. "The enamel painter has to work, not with actual colours, but with mixtures which he only knows from experience will produce certain colours after the operation of the fire." (Aikin.)

=Painting, Encaus'tic.= This method is very ancient, but is now seldom practised. According to Pliny, the colours were made up into crayons with wax, and the subject being traced on the ground with a metal point, they were melted on the picture as they were used. A coating of melted wax was then evenly spread over all, and when it had become quite cold was finally polished.

The art of encaustic painting, after lying dormant for about 15 centuries, was revived by Count Caylus, in 1753. In its new form, the wood or canvas to be painted on is first well rubbed over with wax, and then held before the fire, so that the wax may penetrate and fill up all the interstices, and form a perfectly even surface. The coloured pigments are next mixed with the powder noticed below, which is then rubbed smooth with some thick gum water, and applied with brushes in the same manner as ordinary water colours. When the painting is finished, and quite dry, it is brushed over with pure white wax in a melted state, the surface being equalised by the skilful application of heat; it is, lastly, polished off; as before.

_The powder._--To white wax, melted in an earthen pipkin, add, in small portions at a time, an equal weight of powdered mastic, stirring continuously until the whole is incorporated; then pour it into cold water, and afterwards reduce it to powder in a wedgwood-ware mortar. A small quant.i.ty only of this powder is used with light colours; but more is required with the darker ones, until, on approaching black, the two may be mixed in almost equal proportions.

=Painting, Fres'co.= This method of painting was known to the ancient Egyptians, and was commonly practised by the Greeks and Romans. It is confined to the decoration of the walls of buildings, and is executed by incorporating the colours with the still moist plaster, or gesso. The pigments employed are entirely mineral or vitreous. As it is extremely difficult to alter the work after the colours are once absorbed, or after the ground has hardened, the whole must be carefully designed before commencing the picture, and no more commenced at once than can be executed during the day.

Of all the varieties of painting, fresco is "undoubtedly the most virile, most sure, most resolute, and most durable" (Vasari), and the one most adapted for the purposes of historical painting in its grandest and most exalted forms. In comparison with it, it has been said that even oil painting is "employment fit only for women and children." (Michael Angelo.)

=Painting, Gla.s.s.= See STAINED GLa.s.s.

=Painting, Oil.= This well known and much practised method of painting takes its name from the vehicle employed for the colours. The last may be any of those of a permanent character, and whose natural tint is not altered by admixture with oil. Linseed, nut, and poppy oil, are those which are princ.i.p.ally employed. The first requires the addition of 'driers,' and hence is generally used under the form of 'boiled oil.'

Spirit of turpentine is commonly used to thin down the prepared colours, and the finished picture is frequently covered with a coat of varnish.

=Painting, Por'celain.= See POTTERY, STAINED GLa.s.s, &c.

=Painting, Vel'vet.= Any of the ordinary non-corrosive pigments or liquid colours, thickened with a little gum, may be employed in this art; preference being, however, given to those that possess the greatest brilliancy, and which dry without spreading. See STAINS, &c.

=Painting, Water-colour.= In its strictest and modern sense, 'water-colour painting' means the painting on paper with colours diluted with water. The English school of water-colour painting has produced works which bear comparison with the great masterpieces in oil, and even surpa.s.s them in the delicacy of atmospheric effects. The old practice of making the entire drawing in light and shade by washes of Indian ink or neutral tints, and then adding the various local colours in transparent washes, has given place to the more healthy system of painting every object in its appropriate local colour at the outset.

=PAINTINGS.= Many valuable paintings suffer premature decay from the attacks of a microscopic insect, a species of acarus or mite. The best method of preventing this variety of decay, is to add a little creasote (dissolved in brandy or vinegar), or a few grains each of corrosive sublimate and sal ammoniac (dissolved in a little water), to the paste and glue used to line the picture, as well as to add a few drops of pure creasote or of an alcoholic or ethereal solution of corrosive sublimate to the varnish, when any is to be applied. If the destruction alluded to has already commenced, the painting should be at once carefully cleaned and re-lined, observing to employ one or other of the remedies just mentioned.

The most appropriate and only safe situation in which to keep paintings, is where there is a pure and moderately dry atmosphere. To protect pictures from the effects of damp, it has been suggested to dip the canvas into a solution of silicate of potash, and afterwards dried, previous to its being used. Impure air abounds in carbonic acid and sulphuretted hydrogen. It is the presence of the last in the air that blackens the 'lights,' and causes most of the 'middle tints' and 'shades' to fade; and it is exposure to damp that produces mouldiness and decay of the canvas.

For this reason valuable paintings should not be kept in churches, nor suspended against heavy walls of masonry, especially in badly ventilated buildings. Excess of light, particularly the direct rays of the sun, also acts injuriously on paintings, since it bleaches some colours and darkens others.

The blackened lights of old pictures may be instantly restored to their original hue by touching them with peroxide of hydrogen, diluted with 6 or 8 times its weight of pure water. The part must be afterwards washed with a clean sponge and water. The most astonishing results have been produced in this way. See PEROXIDE OF HYDROGEN.

Pettenkofer observing the colours of many of the oil paintings in the Munich galleries apparently fading, discovered that the dim and grey appearance they then presented, was not really due to any decay of colour, but to a discontinuity of the molecules of the vehicle, and the resinous substances mixed with the pigments; the effect of which was to break up and lessen the ma.s.s of transparent colour and to diminish its intensity.

This separation from each other, of the alternate particles, he conceived was owing to the shrinking and contraction they underwent after long years of exposure to a moist atmosphere. To remedy it Pettenkofer subjected the affected picture to two simple processes, which he is said to have found absolutely successful. The first, which he terms the 'regeneration'